Racks are typically curved after cutting their gear teeth, and a straightening process is required to correct the distortion due to machining. In this study, key factors in the straightening of curved racks by three-point and four-point bending are examined with to automate the correction. The relationship between load and deformation is plotted in real time to determine the unloading point to correct the target deflection for straightening. The parameters constituting the above-mentioned relationship are important for achieving precise correction. The load and deflection at the central loading point are known to be suitable parameters for three-point bending. The smaller the deflection required for correction, the higher is the precision of the displacement sensor required for three-point bending. In the case of four-point bending, the bending moment and bending angle should be selected. In addition, a four-point bending jig is required to load the uniform bending moment during the correction. A modified four-point bending jig is made and the effectiveness was examined.

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